Method of producing fillets in hollow steel propeller blades



em 1, H44.

W. 5 JOHN METHOD OF PRODUCING FILLETS IN HOLLOW STEEL PROPELLER BLADES Filed Dec. 18, 1941 2 Sheets-Sheet l Ffih 1'5, H@44 2,341,784

METHOD OF PRODUEING FILLETS IN HOLLOW siEEL PROPELLBR BLADES W. E. J HN Filed Dec. 18, 1941 2 Sheets-Sheet 2 Patented Feb. 15, 1944 METHdD OF PRODUCING FILLETS IN HOL- LOW STEEL PROPELLER BLADES William John, Williamsport, Pa., assignor to The Aviation Corporation, New York, N. Y.

Application December 18, 1941, Serial No. 423,441

The invention relates to the low steel propeller blades.

In propeller blades for aircraft formed either from tubular blanks or plates welded together, and in which the working portions of the blade are of airfoil cross section, the sharp or-rounded interior corners at the meeting of the two faces which form the leading and trailing edges of the blade increase the stresses at these locations which are apt to exceed the endurance limit of fabrication of hol- 9 Claims. (01. 22-204) coarse grain structure is produced in the steel which tends to set up cracks in the blade when cooled.

One object of the invention is to providean improved method by which fillets wiil'beuniformly produced in the interior corners between V the face-sections of hollow-steel propeller-blades so that they will be of the desired or predetermined form along the interior corners between 10 the blade faces. j Another object of the invention is toprovidethe steel from which the blade is fabricated, and result in fatigue failure. The design loads of the blade makethe sections at the edges critical and the working or breathing of the face sections while in service result in transverse or peripheral loads in addition to the Primary radial loads which accentuate the possibility of fatigue failures. For the purpose of reducing the increase of stresses at these corners, fillets of suitable metal fused to the steel have been found to be beneficial around the inner corners along the edges ofthe blade. The beneficial effect of such fillets depends mainly on their form rather than on the physical properties of the material from which they are made and the modulus of elasticity of the fillet metal must be approximately the same as the steel of the blade. Fillets of this character are produced by melting a suitable alloy in the inside angular corner between the sides of the blade after it has been shaped to airfoil contour, by melting and capillary action. The formation of the fillet is a function of the angle at the meeting corners of the inside faces, which varies at different radial stations of the blade. The ability of the melted metal to flow and form the fillet increases as the angle of the corner decreases. The size of the fillet may be governed,-

within limits, by the amount of the fillet-material that is melted in the regions of varying angles between the faces. The formation of such fillets in propeller blades for maximum efllciency presents difllcult problems because of the curvature of the blade plan forms, the twist in the blade, the formation of the fillet of desired size in the varying angles in the inside corners of .the

blade, and the tendency" of the molten metal to run to the lowest point in the chamber in the blank and overcome by gardless of the position in which the blade is supported. Another difliculty results from the use of brass alloys of relatively high melting point to produce the desired physical properties in the a method of fabricating hollow steel propeller-j blades with fillets in which; the temperature nec j s yto melt the fillet-materia1&1s. j;;- 11 I it will not be substantially higher than-"thegcrltical temperature of the steel used forha'rdening so as to-avoid producing a coarse grain, structure in the steel or setting up cracks in-the blade \whenitisc'ooled. I 1: l

A still further object it: the inventic ln iis 13st )v provide a method by which theflIIet-materiaII-L- will be deposited and distrlbutedin ,the'; blade' j substantially in accordance with the form desired at different radial stations and melted when-itis deposited along the meeting corners ofthe inner faces of the face-sections. Y

, Another object of the invention; isto provide an improved method of producing fillets in hollow steelpropeller blades, in which the'edge portion of the bladeis immersed in a. bath, the tem- :r

perature of which can be controlled within desired limits, for melting the flllet-formingmatej rial and fusing it to the steelin the blade.

Another object of the invention is to provide an improved'method of producing fillets-in hollow steel propeller blades in which-non oxidizing gas to which the fillet-material is -subjected is confined to the interior of the bladeduring the for.- mation of the fillets in the blade.

A further object of theinventionls; to provide a method of forming fillets in hollow steel propeller blades in which the edge-portions ofthe. .blade are successively immersed in a bath for heating it to near melting point of the filletmaterial, to melting temperature, and to cooling gravity the capillarity, re

temperature without displacement of the fllletmaterial, such as a powdeiy] deposited in the corner.

Other objects of the features hereinafter set forth andrnore particufillet. When the blades are heated to a tempera-- I ture considerably above the critical temperature of the steel used in quenching for hardening, a

larly defined by claims at the conclusionhereof. In the drawings, Fig. l is a perspective of the measuring tool used for depositing the brass alloy i asppearirom the detailed descriptio stress-raising effects and of the in powder form into the interior corner of the hollow blade for the formation of an internal fillet. Fig. 2v is a longitudinal section of the hol- 1 low propeller blade with the charge of the filletmaterial deposited into the inner corner along one of the edges of the blade. Fig. 3 is a section taken on line.3--3 of Fig, 2, Fig. 4 is a section taken on line l--4 of Fig. 2, andFig. 5 is a section on line 55 of Fig. 2 after the fillet has been formed in the blade. Fig. 6 is a section showing the plug used for closing and supplying non-oxidizing gas to the chamber in the blade during the melting of the fillet-material. Fig. '7 is a longitudinal section of apparatus used in forming the fillet in the blade. Fig. 8 is a section taken on line 8-8 of Fig. '7.

The invention is exemplified for forming fillets in a hollow steel propeller blade a. Before the fillets are formed the blade is shaped to form a shank a which is adapted to be secured in a propeller hub and usually circular in cross-section, a working portion of airfoil cross-section with a camber member or pressure face a a camber member or suction face a a curved leading'edge a -and a relatively sharp trailing edge a and a tip a". In plan form the leading and trailing edges are longitudinally curved and terminate in a curved closed tip. In some instances the edges are slightly twisted or helical. The

curved or angular interior corners a between the camber members along the leading edge and the relatively sharp angular interior corners between said members along the trailing edge are the places where fillets are desired for reducing size and form for effecting the desired increase of the endurance limit and overcoming fatigue failures.

In carrying out the improved method a measuringtool b is used to deposit the fillet-forming material, which is fluent, such as powder, into one of the interior corners and longitudinally throughout the length of one of theedges of the blade in which the fillet is to be fused. The tool consists of a tapered bar b provided with a longitudinally extending pocket'channel 17 adapted to retain a charge of fillet-forming material Ill. The channel is tapered longitudinally to retain the powder II) in quantities proportionate to the size of the fillet desired at different radial stations of the blade. The shank portion of the blade, which is circular in cross section, isgradually blended into the widest portion of the camber sections and the latter are tapered from the widest portion to the tip. The channel or pocket b is designed to distribute the powder ID along each interior corner of the blade in accordance with the form desired at the different radial stations and in accordance with the angular variations in the interior comers. The tool b, after it has been loaded with the brazing material, is passed through the bore of the shank into the chamber in the blade until it engages, and is longitudinally positioned by, the closed tip. The tool is then turned to invert the pocket b" sothat the powder 10 will be deposited into the interior corner along one edge of the blade as illustrated in Fig. 2. The blade is supported edgewise while the powder In is deposited therein and retained in such position during the subsequent fusing operation. The hollow blade is fabricated to substantially its finished shape, in accordance with any suitable method, before the powder is inserted for the forming of the fillets. As an example oi the fillet-material, an alloy of copper 60 percent, nickel 3 percent, zinc 36 percent, and

tin 1 percent is used which will melt at a temperature slightly higher than, for example 1650' F., the highest temperature required in the sub sequent heat treating of the blank. For example,- if the temperature used in subsequent heat treating of the blade for hardening is 1650 F., the alloy selected for the fillet forming material will have a melting point of about 1700 F.

Next, the bore of the shank of the blade is closed by a plug II which is sweated or brazed into the shank. The plug is provided with an inlet pipe H for the introduction of a nonoxidizing gas into the blade, a valve I2, for controlling the delivery of gas into the chamber in the blade, and an outlet pipe l3. A non-oxidizing gas is used so that subsequent heating operations will not cause oxidizing and scaling of the inside portions of the blade. The supply of gas is regulated by valve l2. By closing the blank,

only the inside of the blade is treated with gas, J

the fillet-material is effected raised to the pre-heated temperature so that no local strains due to the heating will be imparted to the blade. T his pre-heat temperature is lower than that required for fusing the metallic filletforming material, and prepares the blade for expediting the subsequent melting of the filletmaterial.

Next the fillet-formingmaterial is fused into the interior corners of the blade by apparatus which applies localized heat progressively to the inner corner of the blade along the edge which contains the fillet-material while the blade is suspended and passed through a bath. An example of the apparatus usable for this purpose is shown in Figs. 7 and 8. This apparatus comprises a suitable tank 0 provided with an open top, bottom l5, sides [6, ends I1, and transverse partitions l8 and I9 which divide the chamber in the structure into three compartments 0 c and 0 The walls of the structure are made of suitable ceramic or refractory material. The compartments are adapted to contain a suitable bath, such as molten salt, for heating an edge portion of the blade immersed therein. Each compartment is provided with a pair of electrodes 20 to which electric current is supplied of sufficient voltage and amperage to maintain the salt in each compartment at the desired temperature, as hereinafter described. The current supplied to the electrodes for each of the compartments is controlled by suitable devices so that the bath bottom of the openings 2| for immersion of one v edge portion of the blade between partitions l8 and IQ for fusing the fillet-forming material in the blade between said partitions. The temperature of the bath in compartment 0 is higher than the 1200 F. pro-heat temperature of the blade and slightly lower than the temperature required for fusing the fillet-forming material.

For example, if the fusion temperature of the fillet-material used .is about 1700 F., the temperature in compartment may be maintained at approximately 1300 to 1500 F: The temperature of the bath compartment 0 is maintained at a point which will melt the fillet-forming material, for example, 1700 F. The temperature of the salt in compartment 0 is maintained at a sufficientl lower temperature, for example, 1400 F. to cool the fused fillet-material sufficiently so it will harden. As the blade is passed progressivel through the three compartments of the bath, the temperature of the blade is successively elevated in the bath in compartment 0 from pre-heat temperature to a degree approaching the fusion temperature of the fillet-forming materlalyin the bath in compartment 0 to the fusing temperature of the fillet-material, and in the bath in compartment 0 the temperature is "lowered suiiiciently so that the fillet is hardened.

This exemplifies a method in which the temperature of the fillet-material is progressively varied and definitely controlled to raise the temperature almost to the melting point, then increased to the melting point to form the fillet, and then partially cooled so the fillet will solidify and be fused with the steel in, and fill the interior corners of, the blade.

In progressively passing the blade endwise through the bath it is desirable to maintain its edgewise position so that the fillet-forming powder will not be displaced from the point of deposit, and also to tilt the blade to immersethe longitudinally curved edge of the blade to the For this purpose the blade is desired depth. transported so its lower edge will pass through the bath in the tank 0. The blade is secured in clamps 24 adjacent the shank and the tip, respectively, on a carriage which comprises a pair of suspension bars 25 or hangers which carry the clamps, and a link 26 which connects the hangers for simultaneous longitudinal'xmovement and is pivoted to the upper ends of the hangers for independent vertical movement of the shank and tip portions of the blade. The carriage is pro- -vided with a rear roller 21 which travels ,on a

stationary track 2'! and a front roller 28 which is adapted to travel on the stationary track 28.

The tracks are irregularly shaped, as shown, to control the vertical tilting movements of the blade as ,it is propelled forwardly so that the ed e port on adiacent the tip will be first immersed the bath in compartment 0 then moved long tudinally through the bath in compartment 0 and then into and out of the bath in compartg ment 0 As the blade advances. it will be tilte longitud nally by the tracks. so that zonesof the edge of the blade which is longitudinally curved will be progres ivelv immersed in the bath to maintain approximately the same depth of immersion of the edge portion of the blade in. which the fillet is desired. The longitudinal tilt ng of the blade is l mited and is such that the zone of the blade-edge, while passing through t e bath in compartment 0 will be substant ally horizontal so that the melted material will remain substantially in place for localized capillary action.

When powdered fillet-material is used. it will not be substantially displaced from the place where it has been deposited and where the fillet is desired. The carriage is propelled by power from.

an electric motor 33 which is connected through suitable speed-reducing gearing 39 to drive one of the sprocket wheels 32, around which the conveyor 30 passes. The speed of the motor is timed to move the blade through the bath at a predetermined and correct rate of travel, so that the progressive heating, melting and partial cooling will occur while'the blade is immersed in the bath. The link 26, which connects the axles of rollers 21 and 28, is connected to the conveyor by a bracket 34 which is fixed to link 28 and post 35, the lower end of which is pivoted to bracket 34 and the upper end of which is slidable in a lu 36. Said lug is fixed to and movable with the lower reach of the conveyor 30. During the movement of the blade carriage, post 35 is free to slide vertically in lug 36 so that link 26 is free to move vertically and tilt. The tracks 2'! and 28 are designed to guide the carriage and blade so the edge adjacent the tip will be first immersed, the blade will be tilted to immerse its following edge'portion, and so that the zone of the edge portion immersed in the bath in compartment 0 will be nearly horizontal during the melting of the fillet-forming'material to prevent it, when melted, from being dislocated, to immerse the blade in the bath in compartment 0 for 3 be removed from hangers 25 and the blade car-' riage can be propelled to the left tank for re peating the fillet-forming operation to produce a maybe the fillet in the other edge portion of the blade. For this purpose the motor 33 may be of the reversible type. p

The duration of the treatment of the blade in transit through the bath is determined by its speed of travel and ma be regulated. The motor 33 is of the variable speed type and a rheodemo is included in one of the conductors 4|, which supply current to the motor. By varying through this rheostat the resistance in the line which supplies current to the motor, the speed of travel of the chain 30. and the blade carriage varied to immerse the lower edge of the blade in the bath the optimum period for producing the fillet in the blade.

In forming the fillets in the blade, a. charge of fillet-material is deposited by the tool 45 into the inner comer along one of the edges of the blade accordingto the size of the fillet desired at the different radial stations and according to the sharpness of the angle inthe corner from next secured in the clamps 24 on the carria e with the edge into which the fillet-material has been placed lowermost. Valve I2 is then opened to admit hon-oxidizing gas from a suitable source into the chamber in the hollow blade to prevent oxidizing andscaling of the inside of the blade. This is continued during the entire fillet-forming operation. The carriage is started from the left hand endof the tank 0. The motor 33 is then started to advance the. carriage and blade endwise to the right at the correct predetermined speed to complete the formation of the fillet in one edge. During this travel of the blade the edge of the blade near the tip with the inner corner into which the fillet-material has been placed will be first immersed in the bath in chamber 0 the temperature of which is conriage advances mately 1400 F.,

blade inwardly of the and similarly throughout the blade where the internal strains durin v by which the chamber in the blade is utilized to hold non-oxidizing gas during the formation of ior hardening after the therein; by which the melting of the fillet-matetrolled to remain approximately 1500 F. so that the fillet-material and said edge portion will be heated somewhat below the melting point of the fillet-material. As the carriage continues to advance, the lower edge portion of the blade which has been immersed in compartment will pass through the bath in compartment 0 where the temperature is controlled to remain at about 1700" F., to melt the fillet-material in the zone near the tip of the blade and cause it to fuse into the inner comer of the blade by capillary attraction and formthe fillet. As the carfurther, the portion of the blade in which the fillet-material has been fused will pass into the bath in compartment 0 where the temperature is controlled to remain at approxiwhich is suiflcient to partially cool and solidify the fillet. During each forward stroke of the carriage the edge portion of the tip will be progressively immersed, and be heated, melted and cooled until the fillet h has been formed length of the inner corner of the fillet is desired. After the entire fillet has been formed, the tracks 21- 28 will -.guide the carriage to lift the blade out of the .'tank 0. An important attribute of this method is that the zone of the ed e of the blade wherein thegfillet-forming material is melted and as it passes through the bath in compartment 0 will be. substantially horizontal so that the melted material will be retained in its place in the inner corner for capillary action. This substantial horizontality during th melting is maintained throughout the longitudinally curved inner corner of the blade where the fillet is desired. After the fillet has been completed in the interior corner oi one edge of the blade, the blade will be disconnected from the carriage, plug II will be removed, and the same cycle of steps will then be carried outwith fillet-material in the inner corner along the opposite edge of the blade to form thefillet inthat corner. After the fillet ,has been, formed'dn both of the. inner comers alongthe; leading and trailing edges the blade will hardened by quenching at a, temperature of approximately 1650? F.

The invention exemplifies a. method by which fillets are formed in the blade which is first shaped'to'provide a working portion of airfoil contour-longitudinally curved leading and trailing :edges, 9. closed tip and a shank; by which the entire blade :is-pre-heated to avoid setting up the forming of the fillet;

the fillet in a bath; by which the fillet-material may be deposited and distributed into the inner corner throughout the length of the blade in j which the fillet is desired and according to the size desired. at different blade; bywhi'ch a fillet-material is melted at a controlled-temperature only slightlyin excess of I the critical temperature of the steel to avoid producing a coarse, grain structure, or tending to set up cracks in the blade when it is finally quenched fillet has been formed rial is done by progressively immersing the edge portion of the blade in a bath, the temperature of which can be controlled; by which the filletmaterial in a longitudinally curved edge portion radial stations of the by which the edge portions of the blade are progressively immersed in a bath and the temperature successively raised to a point approaching the melting then lowered to cool and solidify the fillet; by which the fillet-forming steps can be expeditiously carried on and controlled to produce uniform fillets in the blades; and by which the fillets of the desired size will be formed throughout the desired extent of the inner corners of the blade.

The invention is not to be understood as restricted to the details set forth, since these may be modified within the scope of the appended claims without departing from the spirit and scope of the invention.

- What I regard as new and desire to claim by Letters Patent is:

1. That improvement in forming a fillet in a hollow steel propeller blade having a working por tion of airfoil cross section. and leading and trailing edges, which comprises uniformly heating the entire blade to a temperature below the meltingpoint of the material, placing fillet forming material in the inside corner along one edge of the blade, successively submerging the edge portion of the blade containing the material in a bath having a temperature higher than the preheat temperature and less than its melting temperature, then in a, bath havinga controlled melting temperature for the material and fusing it to the metal of the blade to form the fillet, and then in a bath having a cooling temperature and movably tlting the blade longitudinally so as to keep said edge portion continuously immersed in and between the baths.

2'. That improvement in forming a fillet in a hollow steel propeller blade comprising a working portion of trailing edges, one of which is longitudinally curved, which comprises placing fillet-forming material in the inside corner along the longitudinally curved edge of the blade, progressively immersing a zone of the edge portion in a bath of suflicient temperature to melt the material and fuse it with the metal of the blade, and automatically tilting the blade during its progression to maintain substantial horizontality of the zone in which the material is being melted and to maintain said edge portion continuously immersed in and between said baths.

- 3. That improvement in forming a fillet in a hollow steel propeller blade having a working portion of airfoil cross section and longitudinally curved leading and trailing edges, which comprises placing fillet-forming material in the inside corner along one edge of the blade, progressively immersing and passing the portions of said edge endwise through a bath of a temperature somewhat below the melting point of the material, then through a bath of sufficient temperature to melt the material and thereby form the" fillet, and then through a bath of cooling temperature continuously moving the blade at a controlled rate longitudinally,-and tilting the blade vertically in a predetermined path so that said edge portion remains continuously immersed through the baths.

4. That improvement in forming a fillet in a portion of airfoil cross section and leading and trailing edges, which comprises placing filletof the blade is melted while it is substantially horizontal so that the melted metal will remain in place and join to the steel by capillary action;

forming material in the inside corner along one edge of the blade, immersing the edge portion around said material in a bath of sufilclent and point, then to the melting point, and p airfoil cross section and leading and forming material ln-the inside corner along one edge of the blade, successively immersing'the edge portion containing said material in a bath having a'temperature somewhat below me melting temperature ofjsaidtrmaterial and then in a bath having a controlled melting temperature for fusing said material with the metal in the blade by progressively-advancing lthe blade longitudinally at a controlled rate while it is immersed in and between said baths and thereby forming a continuous fillet along said inside corner.

6. That improvement in forming a fillet in a hollow steel propeller blade having a working portion of airfoil cross section and leading and trailing edges, which comprises placing filletforming material in the inside corner along one edge of the blade, successively immersing the edge portion containing said material in a bath having a temperature somewhat below the melting temperature of said material and then in a trailing-edges, which comprises placing fillet-.

automatically advancing the blade-longitudinally at a controlled rate with said edge continuously immersed in and between said baths and thereby forming a continuous fillet along said inside corl her, said edge portion being retained continuously submerged while it is subjected to all of said-temperatures.

8. That improvement in forming a fillet in a hollow steel propeller blade having a working portion or airfoil cross section and leading and trailing edges, which comprises placing filletforming material in the inside corner along one edge of theblade, successively immersing the edge-portionaround said material-in a bath having a controlledtemperature somewhat less than the melting point oi' said material, then in a bath having a suiiicient temperature for melting said-material and msing'it with the-metal of the blade and then in a bath having a cooling temperature, advancing the blade longitudinally at a controlled rate while said edge is immersed and automatically tilting the blade longitudinally to keep said edge continuously immersed in and between said baths and thereby forming a continuous fillet along said inside corner.

9. That improvement in forming a fillet in a a hollow steel propeller blade having working porbath having a controlled melting temperature for fusing said material with the metal in the blade by progressively advancing and automatically tilting the blade longitudinally with said edge continuously immersed in and between the bat and thereby forming a continuous fillet along said inside corner.

7. That improvement in forming a fillet in. a hollow steel propeller blade having a working portion of airfoil cross section and leading and trailing edges, which comprises placing filletforming material in the inside corner along one edge of the blade, successively immersing the edge portion around said material in a bath having a controlled temperature somewhat less than the melting point. of said material, then in a bath tions of airfoil cross section and curved leading and trailing edges, which comprises placing fillet-forming material in the inside corner along one edge of the blade, suspending the blade from above at points adjacent its ends so its lower portion throughout its length can be immersed having a sumcient temperaturefor melting said 1 I material and fusing it with the metal of the blade in a bath, successively immersing the lower edge portion containing said material in a bath having a temperature somewhat below the melting temperature of said material, and then in :a bath having a controlled melting temperature for fusing said material with-the metal in the blade,

and finally in a cooling bath by progressively advancing the blade longitudinally and automatically tilting the blade longitudinally by raising and lowerlng of its ends whilesaid edge remains continuously immersed in said baths and thereby forming a continuous fillet along said inside corner. v 1 v I 5 I and then in a bath having a coolin temperature, 

